1. Field of the Invention
The invention relates to the transmission of visual images along optical fibre bundles.
Two types of optical fibre bundle are used: coherent fibre bundles and incoherent fibre bundles.
2. Discussion of Prior Art
Coherent fibre bundles are assembled in such a way that the spatial relationships between fibres are maintained, i.e. there is an exact positional correspondence between the two ends of each fibre in the bundle. Any image transmitted along the fibre therefore remains in its original orientation and is not corrupted.
Incoherent fibres are primarily used as flexible light sources and as such have no requirement for maintaining the orientation of the images transmitted along the fibre. Such light guides are manufactured by assembling the fibres at one end and clamping them, then stretching them out and clamping them at the other end. This process does not require the high levels of accuracy necessary in the manufacture of coherent optical fibres and therefore results in much lower costs. Light guides can also be made in very long lengths (tens of meters) whereas it is difficult to manufacture coherent fibres in such lengths.
It is consequently desirable to be able to calibrate incoherent optical fibre bundles so that they can be used as coherent bundles for the transmission of images.
In this respect various techniques have been proposed. UK Patent Application No. 2082012 concerns a system for a non-coherent fibre-optic bundle image decoder wherein the information on the relative input to output position of each optical fibre is stored, and a computer uses this information to reconstruct an image which has become jumbled in transmission along the fibres. However the relative input to output position for each fibre is determined by interrogating each fibre input with a spot of light, identifying its output position and storing the information. As the number of fibres necessary to produce a reasonably detailed output image has to be large, typically several tens of thousands, this approach is very time consuming. UK Patent Applications Nos. 2092859 and 2124054 also discuss devices using calibrated incoherent optical fibre bundles but as with UK 2082012 calibration is achieved by interrogating single fibres so that determining and storing the fibres positional information is again very time consuming. UK Patent Application No. 2128839 concerns an image display apparatus which uses incoherent optical fibre bundles. In this case the relevant positional information about the fibres is determined by illuminating successive single fibre wide columns of one end of the fibre bundle and noting the output positions of the illumination. Subsequently, and at the same end as the columns were illuminated, perpendicular illumination of successive rows of the fibre bundle, again one fibre wide, is undertaken and the output positional information noted. The combination of the information provided allows the relative input to output position for each fibre in the bundle to be determined. This technique is still very time consuming because a large number of measurements still need to be made for a fibre bundle suitable for image transmission.